Crystal structures of (Z)-(ethene-1,2-diyl)bis(diphenylphosphine sulfide) and its complex with PtII dichloride

The crystal structures of the disulfide derivative of (Z)-ethene-1,2-bis(diphenylphosphine) as well as its complex with PtII are described here. The structure of the phosphine sulfide features intramolecular π–π interactions and C—H⋯S hydrogen bonds, as well as intermolecular π–π and C—H⋯π interactions. The structure of the platinum(II) complex features intermolecular C—H⋯Cl and C—H⋯S hydrogen bonds.


Chemical context
The diphosphine compound cis-bis(diphenylphosphino)ethylene (cis-dppe, Fig. 1) has been used by many research groups as a ligand in organometallic chemistry (Hirano & Miura, 2017;Price & Walton, 1987). While the bisphosphine oxide derivative has found use in the coordination chemistry of both d-block and f-block metals (Jarrett & Sadler, 1991;Banda & Pritchard, 2008;Morse, et al., 2016), the bisphosphine sulfide and bisphosphineselenide derivatives have been less studied. Our group is interested in developing new organic compounds that can facilitate the separation of actinide (An) metals from lanthanide (Ln) metals in liquid-liquid extraction processes (Gorden et al., 2013). Since the An metals have a greater preference for soft-donor atoms than the Ln metals (Cotton, 2006), there have been some successes with the use of phosphine sulfide compounds as actinide extraction agents (e.g. Cyanex 301; Zhu et al., 1996). To this end, we prepared compound I from cis-dppe using elemental sulfur ( Fig. 1; Aguiar & Daigle, 1964;Duncan & Gallagher, 1981). Unfortunately, our efforts in this area were plagued by the ease of isomerization of the cis-alkene to a trans-alkene when the systems were heated for even short lengths of time. In an effort to understand the ability of this ligand to form complexes with metals, we also reacted compound I with Pt(PhCN) 2 Cl 2 to give compound II.

Structural commentary
The structure of compound I was solved in the orthorhombic space group P2 1 2 1 2 1 . The molecular structure of this compound is shown in Fig. 2 along with the atom numbering scheme. The structure of disulfide I has P S bond lengths of 1.9571 (15) and 1.9529 (15) Å , P-C bond lengths that range from 1.804 (4) to 1.824 (4) Å and a C C bond length of 1.338 (5) Å . The P S bonds are oriented in opposite directions with a S1-P1-P2-S2 torsion angle of 166.24 (7) . The 4 descriptor for fourfold coordination around both phosphorus atoms P1 and P2 is 0.94, indicating a near tetrahedral geometry of the phosphine sulfide groups (where 0.00 = square-planar, 0.85 = trigonal-pyramidal, and 1.00 = tetrahedral; Yang et al., 2007). The bond angles around both phosphorus atoms range from 100.75 (18) to 115.48 (14) , with the largest angles involving the sulfur atom. One intra-molecularinteraction is present between the C9-C14 and C21-C26 rings with an intercentroid distance of 3.737 (3) Å , slippage of 3.370 Å and a dihedral angle of 5.6 (2) . Both C8(H8) and C10(H10) are engaged in intramolecular C-HÁ Á ÁS hydrogen bonds with S1 (Ghosh et al., 2020;  The molecular structure of compound I, with the atom-labeling scheme. Displacement ellipsoids are drawn at the 40% probability level using standard CPK colors. Table 1 Hydrogen-bond geometry (Å , ) for I.

Figure 3
A figure depicting the intra-and intermolecular interactions found in crystals of compound I using a ball-and-stick model with standard CPK colors. Hydrogen bonds are drawn using blue dotted lines whileand C-HÁ Á Á interactions are drawn with red dashed lines. Only hydrogen atoms involved in an interaction are shown for clarity. Symmetry codes: (i) Àx + 1 2 , Ày + 1, z + 1 2 ; (ii) Àx + 1, y À 1 2 , Àz + 1 2 .
These interactions have DÁ Á ÁA distances of 3.344 (4) and 3.360 (4) Å with D-HÁ Á ÁA dihedral angles of 113 and 116 , respectively (Table 1, Fig. 3). In a similar fashion, S2 hosts two intramolecular C-H hydrogen bonds with C20(H20) and C26(H26). These interactions have DÁ Á ÁA distances of 3.367 (4) and 3.394 (4) Å with D-HÁ Á ÁA dihedral angles of 113 and 115 , respectively. The Flack parameter for this structure is À0.10 (5) (Parsons et al., 2013). For the Pt II complex II, the structure was solved in the orthorhombic space group Fdd2. Since the entire molecule straddles a twofold symmetry axis, the asymmetric unit is composed of half of the molecule. The complete molecular structure of compound II is shown in Fig. 4 along with the atom-numbering scheme. The Pt-Cl and Pt-S bond lengths are 2.3226 (19) and 2.2712 (19) Å , respectively. The Cl1-Pt1-Cl1 i and S1-Pt1-S1 i bond angles are 90.34 (10) and 97.19 (10) , respectively [symmetry code: (i) Àx + 1, Ày + 1, z]. The 4 descriptor for fourfold coordination around the Pt II center is 0.05, indicating a nearly perfect square-planar orientation of the sulfur and chlorine atoms around the metal (Yang et al., 2007). The P S bond length is 2.012 (3) Å , which is slightly longer than what was observed for compound I. The complex has P-C bond lengths that range from 1.799 (8) to 1.816 (9) Å , with a C C bond length of 1.312 (18) Å . The 4 descriptor for fourfold coordination of the phosphorus atom P1 is 0.91, indicating a slightly distorted tetrahedral geometry of the groups bonded to this atom, and that this tetrahedron is more distorted than what was observed for compound I.

Figure 4
The complete molecular structure of compound II, with the atom-labeling scheme. Unlabeled atoms are related to labeled atoms by a crystallographic twofold axis. Displacement ellipsoids are drawn at the 40% probability level using standard CPK colors (Pt = maroon).

Figure 5
A packing diagram of compound I viewed down the x-axis using a balland-stick model with standard CPK colors. Alland C-HÁ Á Á interactions are drawn with red dashed lines and intermolecular C-HÁ Á ÁS hydrogen bonds are drawn with blue dotted lines. Intramolecular C-HÁ Á ÁS hydrogen bonds and any hydrogen atom not involved in an interaction have been omitted for clarity.
form chains of compound II that run parallel to the z-axis. These chains are then linked into a three-dimensional network through the intermolecular C-HÁ Á ÁS hydrogen bonds.  , 2016). A structure closely related to compound I, where the alkene bears a phenyl ring and is bonded to the phosphine sulfide groups with a trans relationship, has also been deposited in the CSD as a private communication (GOLXAI; Rybakov and Afanas'ev, 2010).

Synthesis and crystallization
Compound I: cis-dppe (500 mg, 1.25 mmol) and elemental sulfur (S 8 , 80 mg, 0.31 mmol) were combined in a roundbottom flask and dissolved in tetrahydrofuran (5 mL). The reaction mixture was stirred for three h at room temperature. The solvent was removed under reduced pressure to give a white, gelatinous solid. The crude product was recrystallized from benzene (5 mL) at 333 K and isolated by vacuum filtration with a Hirsch funnel to give a white solid. Analysis of the solid by 31 P NMR (CDCl 3 ) showed that the target compound I was present along with trans-dppeS 2 and unreacted starting material. Single crystals of compound I grew serendipitously upon slow evaporation of this solution. 31 P NMR (CDCl 3 , 121 MHz): Compound I: 32.3 ppm; trans-dppeS2: 36.6 ppm; cis-dppe: À22 ppm.
Compound II: Equimolar amounts of compound I (10.0 mg, 0.022 mmol) and Pt(PhCN) 2 Cl 2 (10.4 mg, 0.022 mmol) were combined in a small vial and dissolved in 1 mL CDCl 3 . Crystals of compound II formed serendipitously via slow evaporation of the solvent.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. For compounds I and II, all hydrogen atoms bonded to carbon atoms were placed in calculated positions and refined as riding: C-H = 0.95-1.00 Å with U iso (H) = 1.2U eq (C) for vinylic and aromatic hydrogen atoms.

Special details
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

Special details
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.